1. Technical Field
This patent relates to series-fed phased array antennas and in particular to a coupler disposed between the radiating antenna elements of the array and a waveguide having an adjustable wave propagation constant.
2. Background Art
Phased array antennas have many applications in radio broadcast, military, space, radar, sonar, weather satellite, optical and other communication systems. A phased array is an array of radiating elements where the relative phases of respective signals feeding the elements may be varied. As a result, the radiation pattern of the array can be reinforced in a desired direction and suppressed in undesired directions. The relative amplitudes of the signals radiated by the individual elements, through constructive and destructive interference effects, determines the effective radiation pattern. A phased array may be designed to point continuously in a fixed direction, or to scan rapidly in azimuth or elevation.
There are several different ways to feed the elements of a phased array. In a series-fed arrangement, the radiating elements are placed in series, progressively farther and farther away from a feed point. Series-fed arrays are thus simpler to construct than parallel arrays. On the other hand, parallel arrays typically require one feed for each element and a power dividing/combining arrangement.
However, series fed arrays are typically frequency sensitive therefore leading to bandwidth constraints. This is because when the operational frequency is changed, the phase between the radiating elements changes proportionally to the length of the feedline section. As a result the beam in a standard series-fed array tilts in a nonlinear manner.